Solubility compound fertilizer compositions

ABSTRACT

Solid compound fertilizers for dissolving into stock solutions advantageously employing urea phosphate as a phosphorous source. The use of urea phosphate makes it possible to have calcium present as well as nonchelated trace metals without precipitation.

This is a continuation of application Ser. No. 07/989,398 filed on Dec.11, 1992, now abandoned as a continuation of application Ser. No.07/690,099, filed Apr. 23, 1991, now U.S. Pat. No. 5,171,349, filed Dec.15, 1992 which was a continuation-in-part of application Ser. No.07/648,644, filed on Jan. 31, 1991, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns improved solid fertilizer compositions and inparticular solid fertilizer compositions useful for preparing aqueousfertilizer solutions for precision plant nutrition.

2. Prior Art

In greenhouses, nurseries and other intensive horticulture environments,best results are attained when macro- and micronutrients are carefullydelivered to the growing plants. Many growers choose to utilize compoundhigh analysis water-soluble fertilizers. Typically, these fertilizersare marketed as solids which are dissolved to prepare concentrated stocksolutions which are then diluted into irrigation water by means ofproportioners or injection devices.

The Grace Sierra Horticultural Products Company markets a wide range ofwater-soluble solid compound fertilizer formulations under the PetersProfessional® trademark. These formulations are designed to dissolvequickly and completely with no precipitation. It is also desired that afertilizer formulation have good long-term stability as a stock solutionso as not to form precipitates which can clog proportioners andirrigation lines. This has led to a limitation with water-solublefertilizer formulation available heretofore. Calcium is an importantnutrient which is called for in many plant nutrition formulations, butcalcium salts cannot be used together with the conventional phosphoroussources-monoammonium phosphate and diammonium phosphate-as the pHs whichthese phosphate sources provide are too high (not acidic enough) to giveadequate solubility to the calcium ions and thus give rise toprecipitation of the calcium salts in the stock solution and in theproportioners.

Potassium phosphate or sodium phosphate can be used as solublephosphorous sources but these are either expensive or not conducive toplant growth. Phosphoric acid can be used but is a liquid and hazardousto handle. Therefore, a grower wishing to fertilize with both calciumand phosphorous, without resorting to the use of an alkali metalphosphate or liquid phosphorous acid, will need to inject these twoelements separately.

Secondly, and similarly, the use of chelated trace nutrients(micronutrients) has been widely postulated in order to keep these tracenutrients in solution in stock solutions which also contain themonoammonium and diammonium phosphates. If nonchelated micronutrients(such as simple nitrates or sulfates) are employed with the conventionalphosphorous sources, the micronutrients tend to precipitate fromsolution. Again, these chelated micronutrients increase the cost of thefertilizer formulations.

The present invention employs urea phosphate in water-soluble solidfertilizer formulations. Urea phosphate is a known material. The text,Urea and Urea Phosphate Fertilizers by Clifford W. Fowler (Noyes DataCorporation, Park Ridge, N.J., 1976) at page 23, shows a process forpreparing this material and suggests that it may be used as afertilizer. Similarly, U.S. Pat. No. 4,456,463 discloses the use ofureaphosphoric acid reaction products as ammonia-stabilized liquidcomponents of fertilizers. Chemical Abstracts 106(3)101311q shows aliquid component for use in fertilizers which contains a urea phosphatepolycondensation product. Chemical Abstracts 102(9)77486v also showsthis. Other references of interest include Chemical Abstracts101(23)209498s which concerns the biological fate of urea/phosphatefertilizers; Chemical Abstracts 101(21)190398k which discusses the useof urea phosphate fertilizers; Chemical Abstracts 88(19)135558a whichdescribes the reaction of that phosphoric acid reacts with urea and withcalcium salts; and Chemical Abstracts 86(11)70783g which deals with thedevelopment of liquid multicomponent fertilizers based on potassium andammonium nitrates and diphosphates, urea, water and trace elements.

STATEMENT OF THE INVENTION

An improved solid fertilizer which dissolves completely in water to givea phosphorous-containing stock solution has now been found. Thisfertilizer is characterized by being a solid, by having urea phosphateas the principal phosphorous source, by containing calcium and/ormagnesium and/or nonchelated micronutrient trace metals such as iron,manganese, copper, boron, zinc and molybdenum, and by dissolvingcompletely in water without precipitate formation initially or uponprolonged standing, such as for 24 hours or longer.

In one embodiment, this invention provides a calcium-containing solidcomplex fertilizer which dissolves completely in water to give awater-based precipitate-free stable aqueous stock solution, this solidfertilizer containing solid urea phosphate as the principal phosphoroussource and calcium nitrate.

In another embodiment, this invention provides a trace metal-containingsolid complex fertilizer which dissolves completely in water to give awater-based precipitate free stable aqueous stock solution, this solidfertilizer containing solid urea phosphate as the principal phosphoroussource and nonchelated micronutrient trace metal nitrate or sulfatesalts such as at least one of iron sulfate or nitrate, manganese sulfateor nitrate, copper sulfate or nitrate, and zinc sulfate or nitrate. Thismaterial may contain magnesium sulfate or nitrate, as well. It also maycontain calcium nitrate.

In addition, this invention provides a method for preparing a stablewater-based phosphorous-containing and calcium-containing fertilizeraqueous stock solution. This method involves

Obtaining a solid compound fertilizer admixture of urea phosphate as aprimary phosphorous component and calcium nitrate, and

Mixing this admixture with water at a ratio predetermined to yield to aconcentration of the admixture of 2 to 40% by weight and allowing theadmixture to dissolve completely.

This same general process can be used to prepare a nonchelated tracemetal (e.g. FeSO₄, etc.) containing phosphorous-containing fertilizeraqueous stock solution, which also constitutes an aspect of thisinvention.

The inclusion of urea phosphate in a dry blended mixture of nutrientsources which include calcium, and/or magnesium with or without tracemetals such as iron and the like in nonchelated forms such as nitratesand/or sulfates offers several advantages. For one the urea phosphateestablishes a low pH condition when the blended mixture is added towater to make a concentrated stock solution. A stock solution pH in therange of 0 to 2 may be achieved. This low solution pH maintainssolubility and clarity of the concentrated stock solution. Ureaphosphate, by the effect it has on solution pH, prevents the formationof calcium phosphate, magnesium phosphate and iron phosphate, which arenot soluble. Similarly, the low pH helps prevent calcium fromprecipitating in the presence of sulfate ions which may be present.Therefore, when urea phosphate is used as a primary phosphorous source,it will make possible the inclusion of phosphorous and a metal such ascalcium, magnesium or iron in one compound fertilizer, without the useof chelates or the disadvantage of a precipitate forming. This allowsthe end user to prepare and apply a complete nutrient solution using onestock solution and utilizing one injector. It also makes possible theinclusion of nonchelated trace nutrients into phosphorous-containingnutrient solutions without precipitation. It also allows the fertilizersolution to have an increased acidifying effect on the growing medium ifneeded. In summary, the advantages of using urea phosphate as a primaryphosphate source in a solid compound fertilizer are:

a. The ability to purchase, prepare and apply a complete nutrientsolution with one stock solution and one proportioner.

b. The ability to use nonchelated micronutrient trace elements withoutreduction in solubility in the stock solution as is observed usingconventional dry phosphorus sources.

c. The ability to formulate acidic fertilizers that are sold as drysolids and thus are less hazardous to the end user than liquidphosphoric acid-based materials.

DETAILED DESCRIPTION OF THE INVENTION

The fertilizer compositions of this invention are dry solid materials.This is defined to mean that they are particulate flowing solids havinga water content of less than about 10% by weight total composition.

The fertilizer compositions of this invention contain urea phosphate##STR1## as a dry particulate solid. This amount of urea phosphate willvary depending upon the nitrogen and phosphorous analysis desired forthe formulated composition. Typically, the urea phosphate is used inplace of monoammonium phosphate or diammonium phosphate. Since ureaphosphate contributes nitrogen as well as phosphorous in a precisestoichiometric ratio to the dry fertilizer mix, it may be necessary toadd additional phosphorus sources or nitrates or urea as additionalnitrogen sources to alter the ratio provided by urea phosphate alone. Asolid product of the invention will contain at least about 5% by weight(total solids) of urea phosphate which by itself will contribute about2.5%w phosphorous, (calculated as P₂ O₅) and about 1%w nitrogen as N.The solid product can contain up to about 95% by weight of ureaphosphate which would by itself contribute about 43%w phosphorous as P₂O₅ and about 17%w nitrogen as N. Higher P or N assays can be achieved bythe addition of phosphorus sources or various nitrogen sources, such asurea or ammonium nitrate. The range of materials falling within thescope of this invention have phosphorous contents (as %w P₂ O₅) of fromabout 2.5% to 44%, nitrogen contents (as %w N) of from 1% to 40% andpotassium contents (as %w K₂ O) of from 0% to 35%. Within theseformulation ranges and parameters, it is desirable for the ureaphosphate to be the primary or principal source of phosphorous in thepresent solid fertilizers. By "primary" or "principal" source is meantthat urea phosphate contributes at least about 50%, and preferably atleast about 95% and especially essentially 100% of the phosphorouspresent in these products. In cases where urea phosphate is not the solephosphorus source, other phosphates such as potassium phosphate andammonium phosphate can make up the balance.

In addition to the phosphorous and nitrogen and optional potassium, thematerials of this invention include calcium and/or at least one metalselected from magnesium, iron, manganese, copper, boron, zinc andmolybdenum. Ranges of concentration for these materials are as follows:

    ______________________________________                                                    Concentration Range as                                                        Elemental Nutrient in                                             Nutrient    Final Dry Product, %                                              ______________________________________                                        Ca          0-15                                                              Mg          0-5.0                                                             Fe          0-1.0                                                             Mn          0-1.0                                                             Cu          0-0.5                                                             B           0-0.5                                                             Zn          0-1.0                                                             Mo          0-0.2                                                             ______________________________________                                    

Importantly, these materials are not provided as chelates, such as EDTAchelates or the like, but rather as simple salts, especially nitrates orsulfates. In the case of boron, it may be supplied as boric acid.Molybdenum may be provided as an alkali metal or ammonium molybdate.Magnesium, although often present in higher concentration than typicallyassociated with "trace metals" can be present as magnesium sulfate ornitrate. This means that the following representative materials may beused in the products with minimal concern about precipitation or thelike: calcium nitrate, magnesium sulfate, magnesium nitrate, ferroussulfate, ferrous nitrate, manganese sulfate, manganese nitrate, cupricsulfate, cupric nitrate, boric acid, zinc sulfate, zinc nitrate, sodiummolybdate, ammonium molybdate and the like. In addition, the solidproducts can contain additional materials such as cofactors if desired.

These materials are mixed as solids, often with minor amounts of wateras hydration and the like being present to allow a homogenous product tobe formed. The resulting products are dry solids as that term has beendefined herein. They can be sold in bulk or they can be premeasured intounits suitable for forming a standard volume of stock solution. Ineither case, it is often of advantage to distribute the materials inwater-resistant packaging to minimize caking and lumping. Similarly, itmay be of advantage to include soluble inerts which are dyes, or whichpromote dispersion, prevent caking, or the like.

The solid products of this invention are made up into stock solutions bydissolving in water. This should be carried out in clean equipmentusually with some agitation. Commonly, the stock solution contains fromabout 0.5 to about 5 lbs/gallon of dissolved solid (that is, from about2% to about 40% by weight of dissolved solid). Preferably, the stocksolution contains from about 5% to about 35% by weight of dissolvedsolid. This stock solution material is diluted by a factor of from 10 to200 for application to the plants. This gives final concentrationswhich, for nitrogen, range from about 25 ppm up to about 450 ppm, withthe other nutrients scaled accordingly.

The materials of this invention will be further described with referenceto the following examples. These are provided to illustrate the practiceof the invention and not to limit its scope which is defined by theappended claims.

EXAMPLES

Eight pairs of typical stock solutions were prepared using variouscombinations of nutrient sources, and the results differed depending onthe source of phosphate. The nutrient sources included materials whichare commonly used in the manufacture of water-soluble fertilizers. Themost widely used source of phosphorous is monoammonium phosphate (MAP)which was compared with urea phosphate (UP) to determine differences intheir effects on maintaining the solubility of all components of variouscompound fertilizer mixtures. In each pair, one was based on UP and theother on MAP. Some precipitates occurred in the MAP-based materialswithin the first 24 hours and after 30 days, the data in Table 1 wereassembled.

Conclusion

These results show that the use of monoammonium phosphate (MAP) inmixtures with calcium nitrate, magnesium nitrate, ferrous sulfate,manganese sulfate, copper sulfate and zinc sulfate does not maintain thesolubility of these components in solution. This is in contrast to theuse of urea phosphate (UP) which does maintain the solubility of thesein solution consisting of these water soluble nutrient sources. Thesedata show that the use of UP will permit calcium nitrate, magnesiumnitrate and/or metal sulfates to be present in clear, concentrated stocksolutions. This is a result that MAP, as a phosphorus source, isincapable of providing.

                  TABLE 1                                                         ______________________________________                                        EFFECT OF UP ON ELIMINATING PRECIPITATION                                     AS COMPARED TO MAP WHEN MIXED WITH                                            Ca(NO.sub.3).sub.2, Mg(NO.sub.3).sub.2 AND/OR METAL SULFATES                  Precipitate Occurred                                                                              No Precipitate Occurred                                   ______________________________________                                        A.   1 gr of MAP + 100 gr of                                                                          1 gr of UP + 100 gr of                                     calcium nitrate/liter                                                                            calcium nitrate/liter*                                B.   10 gr of MAP + 10 gr of                                                                          10 gr of UP + 10 gr of                                     calcium nitrate/liter                                                                            calcium nitrate/liter                                 C.   100 gr of MAP + 100 gr of                                                                        100 gr of UP + 100 gr                                      calcium nitrate/liter                                                                            of calcium                                                                    nitrate/liter                                         D.   10 gr of MAP + 10 gr of                                                                          10 gr of UP + 10 gr of                                     ferrous sulfate/liter                                                                            ferrous sulfate/liter                                 E.   100 gr of MAP + 100 gr of                                                                        100 gr of UP + 100 gr                                      ferrous sulfate/liter                                                                            of ferrous                                                                    sulfate/liter                                         F.   150 gr of MAP + 150 gr of                                                                        150 gr of UP + 150 gr                                      calcium nitrate + 150 gr                                                                         of calcium nitrate +                                       of magnesium       150 gr of magnesium                                        nitrate/liter      nitrate/liter                                         G.   100 gr of MAP + 100 gr of                                                                        100 gr of UP + 100 gr                                      ferrous sulfate + 30 gr                                                                          of ferrous sulfate +                                       of manganese sulfate + 10                                                                        30 gr of manganese                                         gr of copper sulfate + 40                                                                        sulfate + 10 gr of                                         gr of zinc sulfate/liter                                                                         copper sulfate + 40 gr                                                        of zinc sulfate/liter                                 H.   50 gr of MAP + 95 gr of                                                                          50 gr of UP + 95 gr of                                     calcium nitrate + 1.0 gr                                                                         calcium nitrate + 1.0                                      of ferrous sulfate + 0.5                                                                         gr of ferrous sulfate                                      gr of manganese sulfate +                                                                        + 0.5 gr of manganese                                      0.25 gr of copper sulfate                                                                        sulfate + 0.25 gr of                                       + 0.5 gr of zinc   copper sulfate + 0.5                                       sulfate/liter      gr of zinc                                                                    sulfate/liter                                         ______________________________________                                         *One gram of UP was added to CA(NO.sub.3).sub.2 where CA(NO.sub.3).sub.2      was added at 100, 200, 300, 400, 500, 600, 700, 800, 900 and 1000 grams       per liter of solution and no precipitate occurred in any of the solutions                                                                              

These results show that one can provide solid compound fertilizers whichcan be successfully formed into stable stock solutions having weightcompositions as follows:

    ______________________________________                                                               Preferably                                             ______________________________________                                        A.  Calcium/phosphorous                                                           compound fertilizer                                                       Calcium Nitrate  0.1 to 99%  5 to 95%                                         Urea Phosphate   0.1 to 99%  5 to 95%                                         Other Fertilizer   0 to 75%  0 to 75%                                         Materials                                                                     B.  Calcium/phosphorous/micro-                                                    nutrient compound fertilizer                                              Calcium Nitrate    1 to 99%  5 to 94%                                         Urea Phosphate     1 to 99%  5 to 94%                                         Trace Metal Sulfates                                                                           0.1 to 50%  1 to 40%                                         and Nitrates                                                                  including                                                                     FESO.sub.4                                                                    MnSO.sub.4       especially  2 to 40%                                         ZnSO.sub.4                                                                    CuSO.sub.4                                                                    Other Fertilizer   0 to 75%  0 to 75%                                         Materials including                                                           Mg(NO.sub.3).sub.2 and MgSO.sub.4                                             C.  Phosphorous/micronutrient                                                     compound fertilizer                                                       Urea Phosphate     1 to 99%  5 to 98%                                         Trace Metal Sulfates                                                                           0.1 to 50%  1 to 40%                                         and Nitrates                                                                  including                                                                     FeSO.sub.4                                                                    MnSO.sub.4                                                                    ZnSO.sub.4                                                                    CuSO.sub.4                                                                    Other Fertilizer   0 to 75%  0 to 75%                                         Materials including                                                           Mg(NO.sub.3).sub.2 and MgSO.sub.4                                             ______________________________________                                    

What is claimed is:
 1. A dry solid fertilizer composition consisting ofan unheated admixture of about 1% to about 95% by weight of anon-polymerized dry urea phosphate and about 1% to about 95% by weightof dry calcium nitrate or calcium chloride, said urea phosphate and saidcalcium nitrate or calcium chloride being present in said dry solidcomposition in an amount sufficient to enable formation of a stable,essentially precipitate free concentrated aqueous solution containingabout 2% to about 40% by weight of said fertilizer composition bydissolving said dry solid composition in water.
 2. The dry solidcomposition of claim 1 wherein said urea phosphate is present in saidcomposition in a sufficient amount so that it will be the principalphosphorous source in said concentrated aqueous stock solution preparedutilizing said composition.
 3. The dry solid composition of claim 1wherein said calcium nitrate or calcium chloride is present in saidcomposition in a sufficient amount so that it will be the principalcalcium source in said concentrated aqueous stock solution preparedutilizing said composition.
 4. The dry solid composition of claim 1wherein said urea phosphate is present in said composition in asufficient amount so that it will be the principal phosphorous source insaid concentrated aqueous stock solution and said calcium nitrate orcalcium chloride is present in a sufficient amount so that it will bethe principal calcium source in said concentrated aqueous stocksolution.
 5. The dry solid composition of claim 1 additionally includingat least one non-chelated trace metal salt selected from the groupconsisting of iron, magnesium, manganese, copper and zinc sulfates,chlorides, or nitrates.
 6. The dry solid composition of claim 5 whereinthe non-chelated trace metal salt is present in an amount of up to about50% of the total fertilizer.
 7. The dry solid composition of claim 1additionally including a trace metal salt in a chelated form selectedfrom the group consisting of iron EDTA, DTPA, lignosulfonate, manganese,copper, zinc EDTA, lignosulfonate and mixtures thereof.
 8. The dry solidcomposition of claim 7 wherein the chelated metal salt is present in anamount of up to about 50% of the total fertilizer.
 9. The dry solidcomposition of claim 1 additionally including a non-chelated magnesiumsalt selected from the group consisting of magnesium sulfate, magnesiumnitrate, magnesium chloride and mixtures thereof.
 10. The dry solidcomposition of claim 9 wherein the non-chelated magnesium salt ispresent in an amount of up to abut 50% by weight of the total complexfertilizer.
 11. The dry solid composition of claim 1 comprising 1% to95% by weight of urea phosphate, 1% to 95% by weight of calcium nitrateor chloride and 0.1% by weight of non-chelated trace metal salt.
 12. Adry solid fertilizer composition consisting of an unheated admixture ofabout 1% to about 95% by weight of a non-polymerized dry urea phosphateand about 1% to about 95% by weight of dry calcium nitrate or calciumchloride and about 0.1% to about 50% by weight of a non-chelatedmicronutrient trace metal salt, said urea phosphate and said calciumnitrate or calcium chloride being present in said dry solid compositionin an amount sufficient to enable formation of a stable, essentiallyprecipitate free concentrated aqueous solution containing about 2% toabout 40% by weight of said fertilizer composition by dissolving saiddry solid composition in water.
 13. The dry solid composition of claim12 wherein the non-chelated micronutrient trace metal salt comprisesferrous sulfate, ferrous chloride or iron nitrate.
 14. The dry solidcomposition of claim 12 wherein the non-chelated micronutrient tracemetal salt comprises copper sulfate, copper chloride or copper nitrate.15. The dry solid composition of claim 12 wherein the non-chelatedmicronutrient trace metal salt comprises manganese sulfate, manganesechloride or manganese nitrate.
 16. The dry solid composition of claim 12wherein the non-chelated micronutrient trace metal salt comprises zincsulfate, zinc chloride or zinc nitrate.
 17. The dry solid composition ofclaim 12 wherein the non-chelated micronutrient trace metal saltcomprises magnesium sulfate, magnesium chloride or magnesium nitrate.18. A dry solid fertilizer composition consisting of an unheatedadmixture of about 1% to about 95% by weight of a non-polymerized dryurea phosphate and about 0.1% to about 50% by weight of a sulfate,chloride, nitrate or lignosulfonate salt of a micronutrient trace metalselected from the group consisting of iron, magnesium, manganese, boron,molybdenum, copper and zinc, said urea phosphate being present in saiddry solid composition in an amount sufficient to enable formation of astable, essentially precipitate free concentrated aqueous solutioncontaining about 2% to about 40% by weight of said fertilizercomposition by dissolving said dry solid composition in water.